The present invention relates to a sealing element for an internal combustion engine, preferably a two-stroke engine, having a crankcase with an upper part and a lower part, in which two roller bearings for the crankshaft are disposed between the upper and lower parts, which roller bearings are encircled by rings fashioned out of a heat resistant thermoplastic material.
Two-stroke engines commonly have a crankcase that is split at the level of the crankshaft bearing. The upper part, which has at least one cylinder, is generally cast of light metal alloys, preferably aluminum alloys, which have good thermal conductivity and low weight. To further save weight, the lower parts, which are not subject to such severe thermal strains, are made of thermoplastic materials. Both the great temperature difference between the upper and lower parts of the housing, and the differing coefficients of thermal expansion of the different materials lead to sealing problems. On the other hand, neither gases nor atomized fuel oil can escape into the air.
DE 32 22 457 C3 discloses sealing off a crankcase with the aid of rings made of a high temperature stable man-made polyester material, which are disposed on the crankshaft bearings and are mounted by being pressed against the seats of the roller bearings in the upper or lower part of the crankcase. The sealing of the gap between the upper and lower parts of the crankcase is achieved by means of a sealing frame, to which these rings are affixed and which is tightly fastened between the upper and lower part of the gearbox.
One disadvantage of this arrangement is that the sealing action is insufficient. In addition, both parts of the housing must be machined before assembly to achieve a clean sealing surface for the relatively hard sealing element. A further disadvantage is the relatively large material expenditure for the seal.